Monolithically structured gas discharge device and method of fabrication

ABSTRACT

There is disclosed a gas discharge device having an inherent memory wherein all electrically operative elements are formed on a common support substrate. The device comprises a monolithic panel structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing members, but between two contiguous or adjacent members on the same substrate.

llnited States @atent 1191 Schermerhom MONOLITHICALLY STRUCTURED GAS DKSCHARGE DEVICE AND METHOD OF FABRICATION [75] Inventor: Jerry D. Schermerhorn, Swanton,

Ohio

[73] Assignee: Owens-Illinois, Inc., Toledo, Ohio [22] Filed: Nov. 9, 1971 [21] Appl. No.: 197,003

52 11.8. C1 316/17, 156/3, 313/220 51 Int. Cl. H0lj 9/00 58 Field 61 Search. 29/2516; 315/169 R, 169 TV;

[56] References Cited UNITED STATES PATENTS 3,614,509 10/1971 Willson 315/169 R 3,559,190 1/1971 Bitzer et a1 315/169 R VIEWING COVER PLATE 11/1969 Bergh et al. 156/11 2/1972 Lay 315/169 R Primary Examiner-Charles W. Lanham Assistant Examiner-J. W. Davie I 21 ifb rhey, )1 gm, or Firm fionifldfieml edding, Jim Zegeer & E. J. Holler [5 7] ABSTRACT There is disclosed a gas discharge device having an inherent memory wherein all electrically operative elements are formed on a common support substrate. The device comprises a monolithic panel structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place not between two opposing members, but between two contiguous or adjacent members on the same substrate.

15 Claims, 6 Drawing Figures TOP CONDUCTOR.

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, sou-r 12 MILES l5 ABOUT 6 MILS t .5 TO a MILS TYPICAL ABOUT |.z MILS MONOLITHICALLY STRUCTURED GAS DISCHARGE DEVICE AND METHOD OF FABRICATION BACKGROUND OF THE INVENTION This invention relates to multiple gas discharge devices, especially multiple gas discharge display/memory panels or units which have an electrical memory and which are capable of producing a visual display or representation of data such as numerals, letters, radar displays, aircraft displays, binary-words, educational displays, television, etc. 7

More particularly, this invention relates to a monolithically structured multiple gaseous discharge display/memory panel wherein the conductors or electrodes (for carrying gaseous discharge condition manipulating potentials) are non-conductively coupled to the operative gaseous medium.

Multiple gaseous discharge display/memory devices are now well known in the prior art as exemplified by US. Letters Pat. Nos. 3,499,167 issued to Baker et al. and 3,559,190 issued to Bitzer et al.

An example of a panel structure containing nonphysically isolated or open discharge units is disclosed by the Baker et al. patent. Such a gas discharge display/memory panel, of the Baker et al. type, is characterized by an ionizable gaseous medium, usually a mixture of at least two gases at an appropriate gas pressure, in a thin gas chamber or space between a pair of opposed dielectric charge storage members which are backed by conductor (electrode) members, the conductor members backing each dielectric member typically being appropriately oriented so as to define a plurality of discrete discharge volumes, each constituting a discharge unit.

In some other prior art panels, the discharge units are additionally defined by surrounding or confining physical structure such as by cells or apertures in perforated glass plates and the like so as to be physically isolated relative to other units.

An example of a panel containing physically isolated units is disclosed in the article by D. L. Bitzer and H. G. Slottow entitled The Plasma Display-Panel A Digitally Addressable Display With Inherent Memory, Proceeding of the Fall Joint Computer Conference, lEEE, San Francisco, California, Nov. 1966, pp. 541-647. Also reference is made to hereinbefore cited U.S. Letters Patent 3,559,190 issued to Bitzer et al.

In either case, with or without the confining physical structure, charges (electrons, ions) produced upon ionization of the gas of a selected discharge unit, when proper alternating operating potentials are applied to selected conductors thereof, are collected upon the surfaces of the dielectric at specifically defined locations and constitute an electrical field opposing the electrical field which created them so as to terminate the discharge for the remainder of the half cycle and aid in the initiation of a discharge on a succeeding opposite half cycle of applied voltage, such charges as are stored constituting an electrical memory.

Thus, the dielectric layers prevent the passage of substantial conductive current from the conductor members to the gaseous medium and also serve as collecting surfaces for ionized gaseous medium charges (electrons, ions) during the alternate half cycles of the AC. operating potentials, such charges collecting first on one elemental or discrete dielectric surface area and then on an opposing elemental or discrete dielectric surface area on alternate half cycles to constitute an electrical memory.

In the operation of a gas discharge display/memory panel, a continuous volume of ionizable gas is confined between a pair of dielectric surfaces backed by conductor arrays typically forming matrix elements. The cross conductor arrays may be orthogonally related (but any other configuration of conductor arrays may be used) to define a plurality of opposed pairs of charge storage areas on the surfaces of the dielectric bounding or confining the gas. Thus, for a conductor matrix having H rows and C columns the number of elemental discharge volumes will be the product H X C and the number of elemental or discrete areas will be twice the number of elemental discharge volumes.

In addition to the matrix configuration, the conductor arrays may be shaped otherwise. Accordingly, while the preferred conductor arrangement is of the crossed grid type as discussed herein, it is likewise apparent that where a maximal variety of two dimensional display patterns is not necessary, as where specific standardized visual shapes (e.g., numerals, letters, words, etc.) are to be formed and image resolution is not critical, the conductors may be shaped accordingly.

ln the operation of a multiple gaseous discharge dc vice, of the type described hereinbefore, it is necessary to condition the discrete elemental gas volume of each discharge unit by supplying at least one free electron thereto such that a gaseous discharge can be initiated when the unit is addressed with an operating voltage signal.

The prior art has disclosed and practiced various means for conditioning gaseous discharge units.

One such method comprises the use of external radiation, such as flooding part or all of the gaseous medium of the panel with ultraviolet radiation. This external conditioning method has the obvious disadvantage that it is not always convenient or possible to provide external radiation to a panel, especially if the panel is in a remote position. Likewise, an external UV source requires auxiliary equipment. Accordingly, the use of internal conditioning is generally preferred.

Furthermore, a variety of electronic conditioning means may be utilized.

One internal conditioning means comprises using internal radiation, such as by the inclusion of a radioactive material and/or by the use of one or more so-called pilot discharge unit for the generation of photons.

As described in the Baker et al patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas (discharge unit) to pass freely through the panel gas space so as to condition other and more remote elemental volumes of other discharge units.

However, such internal photon generation and electron conditioning of the panel gaseous medium may become unreliable when a given discharge unit to be addressed is remote in distance (an inch or more) relative to the conditioning source, e.g. the pilot unit. Thus, a multiplicity of pilot units or cells may be required for the conditioning of a panel having a large geometric area.

The gas is one which produces visible light or invisible radiation which stimulates a phosphor (if visual display is an objective) and copious supply of charges (ions and electrons) during discharge.

In an open cell Baker et al type panel, the gas pressure and the electric field are sufficient to laterally confine charges generated on discharge within elemental or discrete dielectric areas within the perimeter of such areas, especially in a panel containing non-isolated units. As described in the Baker et al patent, the space between the dielectric surfaces occupied by the gas is such as to permit photons generated on discharge in a selected discrete or elemental volume of gas to pass freely through the gas space and strike surface areas of dielectric remote from the selected discrete volumes, such remote, photon struck dielectric surface areas thereby emitting electrons so as to condition other and more remote elemental volumes for discharges at a uniform applied potential.

With respect to the memory function of a given discharge panel, the allowable distance or spacing between the dielectric surfaces depends, inter alia, on the frequency of the alternating current supply, the distance typically being greater for lower frequencies.

While the prior art does disclose gaseous discharge devices having externally positioned electrodes for initiating a gaseous discharge, sometimes called "electrodelcss discharge," such prior art devices utilized frequencies and spacings or discharge volumes and operating pressures such that although discharges are initiated in the gaseous medium, such discharges are ineffective or not utilized for charge generation and storage at higher frequencies; although charge storage may be realized at lower frequencies, such charge storage has not been utilized in a display/memory device in the manner of the Bitzer-Slottow or Baker et al invention.

The term memory margin is defined herein as where V, is the half amplitude of the smallest sustaining voltage signal which results in a discharge every half cycle, but at which the cell is not bi-stable and V is the half amplitude of the minimum applied voltage sufficient to sustain discharges once initiated.

It will be understood that the basic electrical phenomenon utilized in this invention is the generation of charges (ions and electrons) alternately storable at discrete points or pairs of opposed or facing discrete points or areas on a dielectric surface or a pair of dielectric surfaces backed by conductors connected to a source of operating potential. Such stored charges result in an electrical field opposing the field produced by the applied potential that created them and hence operate to terminate ionization in the elemental gas volume between opposed or facing discrete points or areas of dielectric surface. The term sustain a discharge means producing a sequence of momentary discharges, at least one discharge for each half cycle of applied alternating sustaining voltage, once the elemental gas volume has been discharged, to maintain alternate storing of charges at discrete areas or pairs of opposed discrete areas on the dielectric surfaces.

In the fabrication of a multiple gaseous discharge display/memory panel, the conductor arrays are applied to supporting substrates, typically of a ceramic or glass material.

Thus in the fabrication of a Baker et al gas discharge display/memory panel, the respective row and column conductor arrays are applied to glass support plates, a

thin dielectric layer or coating then being applied over the conductors in each array. Two or more plates are joined in space relation by a spacer-sealant means so as to form a very thin but large gas discharge chamber which is filled with an operative gas medium.

In a Bitzer et al device, there is fabricated a panel structure wherein the respective row-column conductor arrays are formed, on thin glass plates and a perforated center plate is then sandwiched between the nonconductor surfaces of the thin glass plates with the individual perforations of the center plate positioned at the conductor cross points so as to define discrete discharges.

A number of variations on these two basic approaches for fabrication of gas discharge panel (sometimes called plasma displays) structures have been devised. However, in all cases of which I am aware, the electrically operative elements have been fabricated as separate elements and then assembled in their positionally operative relationship.

In accordance with this invention there is provided a multiple gaseous discharge display/memory panel of a monolithic structure in which the conductor arrays are created on a single substrate and wherein two or more arrays are created on a single substrate and wherein two or more arrays are separated from each other and from the gaseous medium by at least one insulating member. In such a device the gas discharge takes place between two contiguous or adjacent surfaces members formed and carried on the same substrate.

More particularly, in accordance with the present invention, the respective cooperating conductor arrays are formed on and carried by a single common support member, such as a relatively thick non-conductive support substrate. One of the conductor arrays is formed on the surface of the support substrate and then a thin dielectric layer is formed directly on that conductor array. The second conductor array is formed directly on the exposed surface of this dielectric layer to define a plurality of matrix cross points. A plurality of discrete gas cavities, one for each matrix cross point, is formed in the dielectric layer, each cavity in electrically operative adjacency to its corresponding matrix cross point. A further dielectric or non-conductive layer or coating is then applied on the structure thus formed so as to assure that the second conductor array as well as any conductors in the first conductor array are dielectrically isolated from or non-conductively coupled to the operative gas medium with which the cavities are to be filled. Thus all of the electrically operative elements are formed monolithically in permanently fixed positional relationship on a common support substrate. Such structure may be mounted in an envelope filled with an operating gas or a viewing plate may be joined to the structure by a spacer sealant element.

The above and other features and advantages of the invention will become apparent when considered with the following specification and accompanying drawings wherein:

FIG. 1 is an isometric view of a monolithically structured gas discharge device incorporating the invention;

FIG. 2 is a partially enlarged sectional view of the support substrate illustrating the monolithicity of the panel;

FIG. 3 is a diagrammatic illustration of an offset location of the discharge cavities with respect to the cross points of the matrix;

FIG. 4 is a diagrammatic illustration of the position of the discharge cavities overlying the bottom or first applied conductor array as shown in FIG. 2;

FIG. 5 is an enlarged cross-sectioned view of a discharge cavity illustrating a modification of the invention; and

FIG. 6 is an enlarged cross-sectioned view of a cavity shown in FIG. 2 with typical dimensional measurements for a device which has 33 electrodes per inch linear density. Higher densities are contemplated.

Referring to FIG. I, a support substrate 10, which may be flat or planar as shown or bowed or curved if desired, has a first or bottom conductor array 11 formed thereon. Such conductor arrays may be gold, silver, copper etc., as described in Baker et al. US. Pat. No. 3,499,167 and are applied by any suitable conductor printing processes to thicknesses of from about 5,000 to about 10,000 angstrom units. It will be appreciated that such conductors may be small gauge wires which are placed in the desired pattern on the surface of plate 10 and adhered thereto by an adhesive until the later elements of the monolithic structure have been applied.

A dielectric layer or coating 12 is applied over the conductors 11 and has a thickness of from about 0.5 mils to about 6 mils and in an operating example was about 1.2 mils thick. A variety of dielectric materials, especially lead borosilicates, are useful for this purpose and are known in the art.

A top cooperating conductor array 13 is applied to the upper surface of the dielectric coating or layer 12 and can be applied in the same manner as the bottom conductor array 11 (it will be appreciated that the terms top" and bottom are relative and could just as well be called row and column conductor arrays, respectively). Conductor array 13 is applied at transverse angles with respect to conductor array II to thereby define a plurality of matrix cross points.

A plurality of discrete discharge cavities 15 are formed in dielectric coating or layer 12. In the embodiment shown in FIG. 2 and FIG. 4, cavities 15 are located over the bottom conductors ll and adjacent the top conductors 13. Each cavity may be formed by well known photoetching technique and/or chemical etching through a mask or screen having a pattern of holes in registry with the desired cavity location on the dielectric surface. Like-wise, the use of a laser beam, sonic source of like-energy is contemplated for drilling or forming the cavities. The cavities may comprise any suitable geometric shape such as a rounded hole, a groove, etc. In one such case, the mask had openings or apertures having a diameter of about 8 mils and the resulting cavities had exemplary dimensions of about 12 mils diameter at the top and about 6 mils at the bottom with a dielectric layer thickness of about l.2 mils. The etching process in this example was terminated so that a thin layer of about 0.1 to 0.2 mils of dielectric remained on the bottom conductor 11.

As shown in FIG. 3 the cavities need not be located over the bottom conductors or in alignment with any of the conductors but may, in their adjacency to the matrix cross points, only need to be positioned such that the electric field between thecross points is capable of manipulating the discharge condition of any gas in the cavities 15. Thus, the cavities may be located in any of the other sectors adjacent the matrix cross points such as indicated by dotted lines in the upper left corner of FIG. 3. In some cases, it may be desirable to place cavities 15 in all of these positions. It will also be appreciated that cavities 15 may be formed in dielectric layer I2 before or after the application of conductor array 13.

The monolithic portion of the structure is completed by applying, as by vacuum deposition techniques, an overcoat or layer 16 on the top conductor array 13 as well as in the cavities l5 and on the exposed surfaces of dielectric layer 12. The overcoat is typically nonconductive; however, the utilization of conductive overcoats is contemplated. As used herein, the term overcoat is intended to include any film, layer, deposit, etc., applied continuously or discontinuously to the dielectric or conducting surfaces.

The overcoat in addition to providing a coating on conductor array 13 is also preferably a good photoemitter and capable of lowering and stabilizing the operating voltage of the device.

In the practice of this invention, the overcoat typi' cally comprises one or more layers of an oxide of lead, silicon, aluminum, titanium, zirconium, hafnium, magnesium, beryllium, calcium, strontium, or barium. Likewise, oxides of rare earths may be utilized, both of the Lanthanide and Actinide Series, especially scandium, yttrium, thorium, and cerium. For conductive overcoats, pure metals such as zinc, lead, gold, copper, silver, etc. may be used.

Thus, all of the electrically operative structural elements are monolithically formed as an integral assembly. In fact, the electrically operative elements may, if desired, be formed on substrate 10 in such a way as to be removable from the substrate after forming and mounted in a gas filled envelope. However, in one preferred embodiment hereof, a spacer-sealant member [8, such as any well known glass frit sealant is silk screened on the surface of the monolithic assembly, but short of the lateral edges of plate 10 so as to permit the conductors in the arrays to extend to the edges of the plate to permit connection to external circuits. A viewing cover plate 19, is mounted on the monolithic assembly in spaced relation by means of spacer sealant rib 18. It is preferred that the overcoat 16 be limited to the area of the panel where good photoemissivity is desired and not under spacer-sealant 18. The spacing between cover plate 19 and the monolithic assembly is not critical, and forms a gas reservoir or chamber for the assembly. A gas filling tubulation, not shown, may be applied to substrate 10 (outside the viewing area of the device) or to viewing plate 19.

In the prior art, a wide variety of gases and gas mixtures have been utilized as the gaseous medium in a gas discharge device. Typical of such gases include C0; C0 halogens; nitrogen; NI-I oxygen; water vapor; hydrogen; hydrocarbons; P 0 boron fluoride; acid fumes; TiCh; Group VIII gases; air; H 0 vapors of sodium, mercury, thallium, cadmium, rubidium, and cesium; carbon disulfide; laughing gas; H 8; deoxygenated air; phosphorus vapors; C 11 CH naphthalene vapor; enthracene; freon; ethyl alcohol; methylene bromide; heavy hydrogen; electron attaching gases; electron free gases; sulfur hexafluoride; tritium; radio active gases; and the rare or inert gases.

In one embodiment hereof, there is utilized two or more rare gases selected from neon, argon, xenon, krypton, and radon in the presence or absence of effective amounts of other gaseous components such as mercury and/or helium.

A modification in the monolithic structure and manner of forming the cavities is shown in FIG. 5. In this embodiment before applying dielectric layer 12, the bottom conductor array 11 has applied thereto barrier coating which is resistant to the etchant used to form the cavities. Thus, after the dielectric layer 12 has been applied, the etchant removes the dielectric 12 to barrier 20. This avoids any variation in the thickness of dielectric over bottom conductor 11 when the cavities are to be located thereover. Such a barrier 20 may be non-conductive material such as alumina, chrome nitride, etc., deposited by vacuum deposition tecniques to a thickness of about 5,000 to about 10,000 angstrom units.

In the practice of this invention, it may also be feasible to obtain good panel performance without any cavities. In one such embodiment, a photo-emissive ovcrcoat may be employed exclusively over each discharge site or cell, so as to isolate the discharge cell from adjacent or other neighboring cells.

In a further embodiment and modification of this invention, the overcoat is omitted from the top electrode array such that the electrodes are in direct contact with the gaseous medium. In such embodiment, the discharge takes place between the top bare or exposed electrode and the bottom of the cavity.

In a further embodiment hereof, the top and/or bottom electrodes may be split with the cavity positioned in between or within the two halves of the split electrode. The two halves could also be electrically manipulated separately for purposes of addressing (such as with capacitively coupled multiplexing techniques).

In further embodiments of this invention, it is contemplated that other overcoat or barrier layers may be employed, especially luminescent phosphors. Likewise, phosphors may be positioned within the device as dots, etc. so as to be excited by a gas discharge or other means.

The advantages of this invention over present panel structures include:

The discharges take place between the bottom of a depression, under or adjacent to which is a back or bottom conductor and a top conductor covered with a thin film dielectric. The distance between these two points, once established, can be held thru heat treatments and sealing processes even if the entire plate is warped. Prior art construction must hold the distance between the front and back plate accurately, since the discharge occurs between the two plates.

Since the discharge takes place on a single side of a plate, as opposed to between two plates, the front plate 19 is free for other use. The most obvious use is to simply leave it clear for maximum use of light generated in the discharge. This is possible because there are no electrodes or films to block it. Another use is for the application of phosphors.

While the device remains basically an open structure geometry as in Baker et al. US. Pat. No. 3,499,167, some optical isolation and electrical field focusing are obtained. Thus, it is possible to obtain some compromise between good conditioning and ultraviolet crosstalk on color applications.

Electrostatic field focusing is caused by the depression similar to the Bitzer et al sandwich structure. The fields should also be better focused around the front electrodes since they are covered only by a thin dielectric overcoat possibly leading to slightly higher densities.

I claim:

I. A method of making gas discharge display device comprising:

providing a non-conductive support substrate constituting applying a first conductor array to said substrate;

applying a thin dielectric layer on said first conductor array;

applying a second conductor array on said thin dielectric layer in transverse relation with respect to said first conductor array and on the opposite side of said layer;

forming a plurality of gas cavities in said dielectric layer adjacent to but off set from the crossing points of said conductor arrays on the side of said dielectric opposite said first conductor array;

applying a thin overcoat on the surfaces of said dielectric in said cavities and in the side thereof in which said cavities have been formed.

2. The method defined in claim 1 wherein said cavities are formed by etching.

3. The method defined in claim 2 wherein said cavities are formed over said conductors in said first conductor array and the step of terminating said etching prior to exposing said first conductor array.

4. The method defined in claim 3 wherein a barrier layer is applied to the conductors in said first conductor array and said etching is terminated on reaching said barrier layer, and said overcoat is applied to the portion of said barrier layer which is exposed by said etching.

5. The invention defined in claim 1 wherein said dielectric layer has a thickness of from about 0.5 mils to about 6 mils.

6. The invention defined in claim 5 wherein said dielectric layer is lead borosilicate.

7. The invention defined in claim 5 wherein said dielectric layer is about 1.2 mils thick and. that said cavities have a bottom constituted by dielectric material having a thickness of about 0.l to 2 mils.

8. The invention defined in claim 6 wherein said cavities are located over said first conductor array and said dielectric material of 0.1 to 0.2 mil thickness is positioned over said first conductor array.

9. The invention defined in claim 1 wherein the applied overcoat is a non-conductive material.

10. The invention defined in claim I wherein the applied overcoat is a non-conductive photoemissive material.

11. In a method of making gas discharge display device in which:

a non-conductive support substrate has applied thereto a first conductor array, applying a barrier coating on said first conductor array to form a barrier layer, and then applying a thin dielectric coating on said barrier layer to form a thin dielectric layer applying a second conductor array on said support substrate and said thin dielectric layer in transverse relation with respect to said first conductor array and on the opposite sides of said barrier layer;

forming a plurality of cavities in said dielectric layer adjacent to the crossing points of said conductor arrays on the side of said dielectric opposite said barrier layer; applying a thin overcoat on the surfaces of said dielectric in said cavities and in the side thereof in which said cavities have been formed. l2. The method defined in claim 1 wherein said cavities are formed by etching and said barrier layer is formed of an etch resistant material.

13. A method of making gas discharge display device comprising:

providing a non-conductive support substrate constituting: forming a first conductor array on said substrate; applying a thin insulative layer on said first conductor array; forming a transverse conductor array on said thin insulative layer in transverse relation with respect to said first conductor array and on the opposite side of said thin insulative layer; forming a plurality of gas cavities in said thin insulative layer offset from but proximate to the crossing points of said conductor arrays on the side of said insulative layer opposite said first conductor array;

applying a thin non-conductive overcoat on the surfaces of said thin insulative layer in said cavities and in the side thereof in which said cavities have been formed,

applying a sealant rib to the surface of said substrate,

joining a viewing cover plate to said sealant rib, and

filling the cavities in said device with a gaseous medium.

14. The invention defined in claim 13 wherein said gaseous medium is constituted by two or more rare gases selected from the group neon, argon, xenon, krypton and radon.

15. The invention defined in claim 14 wherein said gaseous medium includes effective amounts of other gaseous components selected from mercury and helium. 

1. A method of making gas discharge display device comprising: providing a non-conductive support substrate constituting applying a first conductor array to said substrate; applying a thin dielectric layer on said first conductor array; applying a second conductor array on said thin dielectric layer in transverse relation with respect to said first conductor array and on the opposite side of said layer; forming a plurality of gas cavities in said dielectric layer adjacent to but off set from the crossing points of said conductor arrays on the side of said dielectric opposite said first conductor array; applying a thin overcoat on the surfaces of said dielectric in said cavities and in the side thereof in which said cavities have been formed.
 2. The method defined in claim 1 wherein said cavities are formed by etching.
 3. The method defined in claim 2 wherein said cavities are formed over said conductors in said first conductor array and the step of terminating said etching prior to exposing said first conductor array.
 4. The method defined in claim 3 wherein a barrier layer is applied to the conductors in said first conductor array and said etching is terminated on reaching said barrier layer, and said overcoat is applied to the portion of said barrier layer which is exposed by said etching.
 5. The invention defined in claim 1 wherein said dielectric layer has a thickness of from about 0.5 mils to about 6 mils.
 6. The invention defined in claim 5 wherein said dielectric layer is lead borosilicate.
 7. The invention defined in claim 5 wherein said dielectric layer is about 1.2 mils thick and that said cavities have a bottom constituted by dielectric material having a thickness of about 0.1 to 2 mils.
 8. The invention defined in claim 6 wherein said cavities are located over said first conductor array and said dielectric material of 0.1 to 0.2 mil thickness is positioned over said first conductor array.
 9. The invention defined in claim 1 wherein the applied overcoat is a non-conductive material.
 10. The invention defined in claim 1 wherein the applied overcoat is a non-conductive photoemissive material.
 11. In a method of making gas discharge display device in which: a non-conductive support substrate has applied thereto a first conductor array, applying a barrier coating on said first conductor array to form a barrier layer, and then applying a thin dielectric coating on said barrIer layer to form a thin dielectric layer applying a second conductor array on said support substrate and said thin dielectric layer in transverse relation with respect to said first conductor array and on the opposite sides of said barrier layer; forming a plurality of cavities in said dielectric layer adjacent to the crossing points of said conductor arrays on the side of said dielectric opposite said barrier layer; applying a thin overcoat on the surfaces of said dielectric in said cavities and in the side thereof in which said cavities have been formed.
 12. The method defined in claim 1 wherein said cavities are formed by etching and said barrier layer is formed of an etch resistant material.
 13. A method of making gas discharge display device comprising: providing a non-conductive support substrate constituting: forming a first conductor array on said substrate; applying a thin insulative layer on said first conductor array; forming a transverse conductor array on said thin insulative layer in transverse relation with respect to said first conductor array and on the opposite side of said thin insulative layer; forming a plurality of gas cavities in said thin insulative layer offset from but proximate to the crossing points of said conductor arrays on the side of said insulative layer opposite said first conductor array; applying a thin non-conductive overcoat on the surfaces of said thin insulative layer in said cavities and in the side thereof in which said cavities have been formed, applying a sealant rib to the surface of said substrate, joining a viewing cover plate to said sealant rib, and filling the cavities in said device with a gaseous medium.
 14. The invention defined in claim 13 wherein said gaseous medium is constituted by two or more rare gases selected from the group neon, argon, xenon, krypton and radon.
 15. The invention defined in claim 14 wherein said gaseous medium includes effective amounts of other gaseous components selected from mercury and helium. 